In the prior art, broadband resistive microwave mixers using field effect transistors (FETs) or bipolar junction transistors (BJTs) have frequency bandwidths that are limited by in-band self-resonance on the gate or base side, respectively. This self-resonance typically happens due to the resonance of a capacitance of a gate or base and an inductance of a micro-strip routing line.
Conversion loss for a mixer is defined as the ratio of the power at the output frequency to the power at the input frequency with a given local oscillator (LO) power. In the prior art, because of the self-resonance, the conversion loss is worse at the resonance frequency. Further the handling power of a mixer proportionally decreases with the frequency bandwidth, because one way to reduce the capacitance of the gate or base to increase frequency bandwidth is to reduce the size of the FET or BJT, which reduces the power handling capability.
In the prior art distributed mixers are another approach to achieve a broadband mixer. Distributed mixers use multiple small cells along with multiple sections of transmission line and terminate the local oscillator (LO) and radio frequency (RF) nodes with approximately 50 Ohm resistors. However, these distributed mixers are very complex and need a large space to interconnect the active devices in each stage active by using long micro-strip transmission lines. Besides the waste of large space and complexity, these long micro-strip transmission lines are another source of ohmic loss. Another disadvantage of the distributed mixer approach is that the RF node termination resistors dissipate RF power and increase conversion loss.
Such a distributed mixer, as shown in FIG. 1, is described by Amin Q. Safarian, Ahmad Yazdi and Payam Heydari in “Design and Analysis of an Ultrawide-Band Distributed CMOS Mixer” IEEE Transactions on Very Large Scale Integration Systems, Vol. 13, No. 5, May 2005. The inductors shown in FIG. 1 correspond to micro-strip routing lines.
What is needed is a broadband mixer that has low conversion loss over a broadband frequency. Also needed is a broadband mixer with high power handling capability. The embodiments of the present disclosure answer these and other needs.